May 2009


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Ellery Frahm <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Thu, 21 May 2009 07:19:42 -0500
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Moderator: Ellery Frahm, [log in to unmask],
Electron Microprobe Lab, University of Minnesota

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Hi Ron,

What about the beam position on the sample?  Is that stable?  If, for  
example, there is charging in the objective lens pole piece or  
somewhere else in the column, the beam could wonder a lot across the  
sample, constantly changing the Bragg angles (and therefore L values)  
and affecting all the spectrometers.


On May 20, 2009, at 11:49 PM, Ron Rasch wrote:

> Hi Ellery,
> Yes all good questions. To go into more detail:
> This probe has seen a lot of work, 15 years of 24 hrs a day, 7 days  
> week, excluding down time etc.
> Doing a peak search during Qnt analysis, does not help anymore, but  
> it use to when it started "going off". For most of the probe's life  
> I only did a peak search during Standard analysis.
> All four WDS spectrometers are giving bad results but to a greater  
> or lesser extent.
> My FCS is probably the best and my H type is probably the worst.
> The beam current looks very stable.
> The standards are good and have been tested in my new probe. Plus  
> they were good at the start (15 years ago).
> There seems to be no strong connection between L value and  
> reproducibility, some days the high values some days the low, but  
> mostly the low L_values are better.
> I've had the factory check the base plate, align the crystal tilt  
> and do the SCA conditions, twice.
> I do not believe it's the x-ray detectors (see below), but just in  
> case I've replaced one Xe detector and the window for one GPC, no  
> great improvement.
> My usual test (apart from just doing a typical analysis) is to do a  
> peak search on a standard, then take a 10 second count three times,  
> then move off the peak then repeat.
> On any given peak search, the three count rates are quite consistent  
> with each other, just not consistent with the count rates after the  
> next peak search. Two very close peak positions may not yield  
> similar count rates.
> Next on my list is to try swapping a stepper motor and gear box with  
> my new probe, but I'm also looking for any other ideas or things to  
> check.
> Cheers,
> Ron